The present invention relates to a method of granulating powder and an apparatus for granulating powder and, more specifically, to a method of granulating powder applied in the manufacture of granulated or powdery products such as pharmaceuticals, food, agricultural chemicals, ceramics, etc. (hereinafter referred to as "granule" or "granulated product" in some cases) and an apparatus for granulating powder.
Fine powder the particle diameter of which is several .mu.m or under is generally light and easily dispersed although there is also heavy powder such as metallic powder, and the fine particles which fly up have strong adhesion to the inner face a of container, etc. of a fluidized bed granulating apparatus.
Moreover, such light fine powder is poor in fluidity and cannot form the necessary fluidized bed for performing fluidized bed granulation, for example. This is because all of the powder cannot be moved if the fluidizing air capacity for fluidized bed granulation is small but, as the air capacity is gradually increased, the powder suddenly flies up like smoke, and it is impossible to find any proper air capacity for fluidization.
Also, the flied-up light fine powder can adhere to the inner face of the container, etc. of the fluidized bed granulating apparatus and gradually accumulates there. This deposition is not easily removed. So the light fine powder cannot be mixed, much less granulated in fluidized bed granulating apparatuses.
Furthermore, such light fine powder, which has a strong flocculating performance in addition to the abovementioned nature, often forms a flocculated lump consisting of hundreds to thousands of primary particles, and it is impossible to coat all of the primary particles with a binder because the flocculated lump cannot be dispersed into individual primary particles with the various granulating methods currently put into practice.
Therefore, granules formed by this method has the problem of being easily destroyed because it contains flocculated lumps without binder inside.
In addition, in the case where compression moldings (tablets) are made by using this granule containing flocculated lumps without binder inside, the flocculated lumps inside the granule change, under pressure, into hard lumps which are not easily dispersed at the time of dissolution. This is due to the absence, between primary particles, of any binder which serves as a dispersing agent at the time of dissolution, and such phenomenon spoils the effect or meaning of pulverization of raw material, etc. made for any specific purpose such as improvement of solubility, for example.
As described above, it has so far been considered impossible to perform fluidized bed granulation of light fine powders or to perform fluidized bed granulation while coating individual particles constituting flocculated lumps which consists of light fine powder with a binder.